Hyponatremia in multiple myeloma is

Pseudohyponatremia Patients with multiple myeloma also have a decreased anion gap because of the M component is cationic, resulting in retention of chloride This is often accompanied by hyponatremia that is felt to be aificial (pseudohyponatremia) because each volume of serum has less water as a result of the increased protein Ref: Harrison's 19th edition Pgno : 714